1. Field of the Invention
This invention relates in general to the field of electronic devices, and more particularly to an apparatus and method that provides for efficient two-way optical communication where an optical transmitter may interfere with a corresponding optical receiver.
2. Description of the Related Art
It would be very difficult today to find a consumer electronic device which does not have one or more light emitting diodes (LEDs) disposed therein to indicate status (e.g., on, off, message waiting, etc.) to a user. LED indicators are used not only in consumer devices, but also in devices in the business and transportation realms.
As a result, a significant amount of attention in the art has been devoted to decreasing the cost of manufacture of devices with one or more LED indicators. More specifically, light pipes (also referred to as “light tunnels” or “light tubes”) have been developed to enable the light from one or more LEDs mounted on a circuit board in a device to be transported efficiently to an area of a display where the light is required, thus eliminating a significant amount of hand labor that would otherwise be required to fabricate a product. As one skilled in the art will appreciate, light pipes are generally manufactured from plastic materials that transport light via a reflective lining, or transparent solids that transport the light by total internal reflection. As such, the pipes, according to configuration, are snapped into place on a circuit board, and the board is mounted behind a panel or display.
In addition to being used to display state or status of a given device, light pipes are used to receive light transmitted from outside of the given device and to route the light to light sensors internal to the given device. Such an application can be as simple as sensing ambient light in order to control brightness of a display, or it may be more complex, such as receiving an optical commissioning data stream from another device in order to configure the given device for operation.
For devices that require two-way (i.e., transmit and receive) optical communication, like lower frequency devices, it is important to isolate transmit circuits from receive circuits in order to preclude the transmit circuits from interfering with the receive circuits. In many instances, isolation amounts to placement of opaque materials such as black tape in more prevalent interference paths. But the isolation issue becomes much more prevalent when a single light pipe is shared by transmit and receive circuits, as is the case in consumer devices where size and weight are critical design constraints.
To address isolation in a shared light pipe, one approach requires that transmit circuits and receive circuits be of such disparate optical wavelengths that transmissions from the transmit circuits are essentially undetectable by the receive circuits. But this approach is not very practical in consumer devices that employ inexpensive optical sensors (e.g., photodiodes) that sense over a broad optical spectrum.
As a result, special purpose light pipes have been developed that route light to/from a single position on a display, but that allow for separation of a corresponding light source and light sensor that share a single light pipe. For example, in U.S. Pat. No. 7,352,930, Lowles discloses a shared light pipe for message indicator and light sensor on a mobile communication device that is of the so-called “Y configuration.” A transmit circuit is disposed on one leg of the Y and a receive circuit is disposed on the other leg of the Y, thus allowing for separation between the transmit circuit and the receive circuit, and also allowing space to place masking material between the circuits. Interference is still significant within the pipe, and Lowles teaches that it is prudent to only sense light when the light is not being transmitted by the transmit circuit, unless it is desired to confirm the presence of the transmit circuit. Such a configuration, however, is simplistic in nature, and does not lend itself to applications other than using a shared light pipe to sense light when a message waiting indicator is not on.
More particularly, consider a situation where it may be required to employ a shared light pipe to transmit constant illumination or a blinking indicator, while simultaneously being required to receive an optical data stream from, say, a commissioning device or a controller. To employ Lowle's technique would require an inordinate amount of time to receive the optical stream, or it would require that the optical stream bit rate be on the order of minutes.
Accordingly, what is required is an apparatus and method that provides for two-way optical communication using a shared light pipe that supports optical bit rates much faster than what has been heretofore provided, where transmissions must be reliably perceived by a user (i.e., the human eye).
In addition, what is needed is a mechanism that provides a constant illumination or visibly perceptible indication of device state, which may also receive an optical data stream via a shared light pipe.
Finally, what is needed is a method for using a shared light pipe to transmit illumination or visibly perceptible device state to a user, while simultaneously receiving optical data from another device.